Recently, the distances between adjacent word lines and between adjacent bit lines are more narrow as the device is further miniaturized. That is, the distance between memory cell transistors is narrow. Therefore, for example, if data is written into a memory cell transistor in which binary data is held, the threshold distribution of a memory cell transistor in which data has been already written varies due to variation in the threshold distribution of a memory cell transistor adjacent to the above memory cell transistor. In the following description, the variation in the threshold distribution is referred to as a coupling effect.
Therefore, the threshold value of the memory cell transistor is raised from the initial read level and it becomes necessary to transfer a higher voltage in order to turn on the memory cell transistor. That is, a voltage generator circuit that generates plural voltages is required. In Jpn. Pat. Appln. KOKAI Publication No. H11-134892, voltage generator circuits whose current supply rates are different are described.
In this case, if the above high voltage is transferred to the control gate of a memory cell transistor adjacent to a memory cell transistor before the high voltage is transferred to the control gate of the latter memory cell transistor, gate induced drain leakage (GIDL) will occur between the impurity diffusion layer and the memory cell transistor.